The invention relates to a scanner for generating chrominance component signals, comprising an illumination device for illuminating or transilluminating an image, monochromatic light sources and scanning elements for converting the light obtained from the illuminated or transilluminated image into a chrominance component signal. The invention particularly relates to a telecine for scanning cinematographic film material.
Telecines comprise, for example, CCD elements for scanning a film, in which the film to be scanned is generally illuminated or transilluminated with a halogen or xenon light source. In a telecine, the film is transported along a color camera by means of a film transport device. To generate a color signal composed of three chrominance components, three sensors are used in the color camera, in which prepositioned color filters make each sensor sensitive in only one given spectral range. The film frame is imaged either via prism splitters on sensors which are arranged at different positions, or three sensors arranged on a chip and accommodated in a housing are illuminated. Such trilinear sensors have housing-integrated color filters for separating the colors. They provide the advantage of a small required surface area and a reduced number of components for mechanical adjustment.
A problem in these arrangements is that the sensors have different spectral sensitivities so that the power of illumination is adjusted in accordance with the most sensitive sensor. As a result, the separate sensors must be driven separately. To avoid this, U.S. Pat. No. 5,392,080 proposes, in a telecine with image-sequential alignment and scanning, to provide an illumination device constituted by three monochromatic light sources for the purpose of illumination, in which the intensity of each light source can be adjusted independently of the other light sources. Before illuminating the film to be scanned, the light currents of these light sources are mixed in a spherical integrator to a single, diffuse light current.
However, the problem still remains that the spectral sensitivity of a sensor may have maximal side values in neighboring spectral ranges, so that crosstalk may still occur in the individual sensors, in spite of the three monochromatic light sources.
It is an object of the invention to provide a solution in which the sensors supply exclusively chrominance component signals of their respective chrominance components.
This object is solved in that the illumination device is implemented in such a way that the monochromatic light sources illuminate the film frame at positions which are separated from each other, and the sensors are arranged in such a way that they are illuminated exclusively by the relevant associated light source.
The invention has the advantage that crosstalk between the separate chrominance components is completely excluded at the pick-up side by the mechanical construction of the light guidance of the monochromatic light sources used for illumination, because each sensor is illuminated by only one of the light sources. The invention has the further advantage that color filters need not be positioned in front of the sensors. Since each color filter attenuates the light to be passed to a certain extent, the power of illumination can be reduced accordingly.
In a further embodiment of the invention, the separate light sources of the illumination device are constituted by laser light sources. Since laser light is strictly monochromatic, color crosstalk is also avoided at the illumination side, as contrasted to light sources in which the monochromaticity is dependent on the quality of the filters used.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.